Sleep mode systems allow electronic devices to enter a state of low energy use, such as where battery conservation is preferable without deleting cache or ending running program states, for example. In the specific case of laptop computers and other clamshell type electronic devices, a resident sleep mode system can detect whether the computing device is closed and put the device into sleep mode automatically. The sleep mode system may also put the device back into a wake mode when the device is opened. Unfortunately, many conventional sleep mode systems for electronic devices can be inaccurate and are sometimes fooled into activating or switching modes at the wrong times. For example, sleep mode systems using Hall Effect sensors detect when a magnet in a lid or base is relatively near or far away from a corresponding sensor in an opposing base or lid. This type of system can be triggered by other magnets in close proximity to the electronic device, however, resulting in unwanted mode switches. Hall Effect sensors are also relatively inaccurate, such that ordinary part and manufacturing tolerances can result in finished products having varying reliance and sensitivity levels. While sleep mode systems for electronic devices have worked well in the past, there can be room for improvement. Accordingly, there is a need for improved computer sleep mode systems that are more accurate and less foolproof than existing systems.